1. Industrial Field of the Invention
The present invention relates to a filler neck cap for a fuel tank of an automobile or the like.
2. Description of the Prior Art
A conventional filler neck cap comprises an outer cap which is turned manually and an inner cap to be inserted in a filler neck. The conventional filler neck cap is of the type in which a turning force is transmitted from the outer cap to the inner cap and a torque applied to the inner cap is limited by means of a ratchet and a latch. In such filler neck caps, it is generally held that an operating torque or a force of turning the outer cap by a hand is substantially equal to a tightening torque or a force of screwing the inner cap. The filler neck cap of the aforesaid type has been disclosed in, for example, U.S. Pat. Nos. 4,676,390, 5,020,685, 5,183,173, 5,203,466, Japanese Patent Unexamined Publication No. 59-209547 (1984) or the like. Further, there is a filler neck cap including a valve of the pressure release type or the auto venting type in which the pressure is automatically released when the pressure in the tank becomes abnormally high. In the above filler neck cap, airtightness at the filler neck is established by pressing an O-ring fitted on the inner cap against an inner peripheral surface of the filler neck when the filler neck cap is screwingly inserted in the filler neck. For these reasons, when the manually tightening torque applied to the inner cap is insufficient, gas leakage may occur before the valve of the pressure release type or of the auto venting type fulfills its function.